Showing papers by "Rowett Research Institute published in 1979"
TL;DR: In this paper, a method for estimating the percentage of dietary protein that is degraded by microbial action in the rumen when protein supplement is added to a specified ration is proposed, where the potential degradability, p, is measured by incubating the supplement in artificial-fibre bags and is related to incubation time, t, by the equation p = a+b (1 − e -ct ).
Abstract: A method is proposed for estimating the percentage of dietary protein that is degraded by microbial action in the rumen when protein supplement is added to a specified ration. The potential degradability, p , is measured by incubating the supplement in artificial-fibre bags in the rumen and is related to incubation time, t , by the equation p = a+b (1 – e -ct ). The rate constant k , measuring the passage of the supplement from the rumen to the abomasum, is obtained in a separate experiment in which the supplement is combined with a chromium marker which renders it completely indigestible. The effective percentage degradation, p , of the supplement, allowing for rate of passage, is shown to be p = a +[ bc/(c+k) ] (1- e -(e+k)t ) by time, t , after feeding. As t increases, this tends to the asymptotic value a+bc /( c+k ), which therefore provides an estimate of the degradability of the protein supplement under the specified feeding conditions. The method is illustrated by results obtained with soya-bean meal fed as a supplement to a dried-grass diet for sheep. The incubation measurements showed that 89% of the soya-bean protein disappeared within 24 h and indicated that it was all ultimately degradable with this diet. When the dried grass was given at a restricted level of feeding the allowance for time of retention in the rumen reduced the estimate of final degradability to 71% (69% within 24 h). With ad libitum feeding there was a faster rate of passage and the final degradability was estimated to be 66% (65% within 24 h).
4,552 citations
TL;DR: When TVP was fed to rats as the only protein source, they had significantly lower growth rates and plasma Zn concentrations than rats given an egg-albumen-based diet of similar Zn content.
Abstract: 1. A study has been made of the zinc, copper, iron, manganese, protein (nitrogen X 6.25) and phytic acid contents of nineteen soya-bean-based textured-vegetable-protein (TVP) meat-extenders and meat-substitutes and of three "ready-prepared" canned meals containing TVP. 2. Phytate analysis was performed using a newly-developed method based on Holt's (1955) procedure. This method enabled the phytate content of milligram quantities of TVP to be estimated, with an SD for six replicates of 3%. 3. The Fe, Cu and Mn contents (mg/kg) of the meat extenders or meat-substitutes varied, with values of 59.4-144, 14.1-19.7 and 19.5-29.1 respectively. The protein content of these products was approximately 500 g/kg. 4. The phytate content of the meat-extenders and meat-substitutes ranged from 11.0 to 20.2 g/kg and the Zn content from 35.0 to 49.4 mg Zn/kg. The calculated molar ratio, phytate: Zn varied from 25 to 42. 5. The trace element, phytate and protein contents of the "ready-prepared" canned meals were 30-50% lower than the meat-extenders and meat-substitutes. 6. Cooking the "ready-prepared" meals as specified by the manufacturers was without effect on the trace element or phytate content. 7. When TVP was fed to rats as the only protein source, they had significantly lower growth rates and plasma Zn concentrations than rats given an egg-albumen-based diet of similar Zn content (14.5 mg Zn/kg). Supplementation of the TVP diet with Zn (100 mg Zn/kg) significantly increased growth rate and plasma Zn concentration whereas Zn supplementation of the albumen diet was without effect. 8. The possible implications of consumption of TVP products in relation to Zn status of the human population is discussed.
262 citations
TL;DR: Phytate naturally present in TVP behaves similarly to phytate added to an otherwisephytate-free diet and that the reduced availability of Zn inTVP diets can be accounted for entirely by their phytates contents.
Abstract: 1. Studies were carried out in vitro to examine the effects of phytate on the solubility of the trace elements zinc, copper and manganese. Appropriate volumes of a solution of sodium phytate were added to a mineral solution to achieve phytate: Zn values of from 0 : 1 to 45 : 1. In a second series the same values for phytate: Zn were achieved by varying the amount of added Zn at a fixed phytate concentration. 2. In both experiments greater than 85% of the Zn was rendered insoluble at pH 6.5 even at the lowest value for phytate: Zn (5 : 1). The effect of phytate on Zn solubility was greater than effects on Cu or Mn. 3. In a dietary study, rats were offered a semi-synthetic egg-albumin-based diet with added phytate. Two series of diets were prepared, the first had a constant Zn content (18.5 mg Zn/kg) and the amount of sodium phytate varied so as to achieve values for phytate: Zn of from 0 : 1 to 40 : 1 (series 1). In the second series, the same values for phytate: Zn were achieved by adding a fixed amount of phytate (7.4 g phytic acid/kg) while the amount of Zn was varied (series 2). 4. Dietary phytate caused significant reductions in growth rates, plasma Zn concentrations and hair Zn concentrations and greying of the coat at values for phytate: Zn of 15 : 1, 10 : 1, 15 : 1 and 15 : 1, respectively. 5. While phytate was apparently slightly more effective in reducing Zn status when phytate: Zn values were achieved at the lower absolute levels of phytate and zn (series 1 diets), the differences at equivalent phytate: Zn values were small. It was concluded that phytate: Zn values can be used as an indicator of Zn availability from phytate-rich diets. 6. Rats offered three diets containing soya-bean-based textured-vegetable-protein (TVP) exhibited low rates of weight gain compared with rats offered an egg-albumen-based diet of similar Zn content (14.5 mg Zn/kg). Additional Zn supplied in drinking-water (25 mg Zn//l) was without effect on rats consuming the egg-albumin diet but significantly improved the weight gain of rats on the TVP diets. 7. It was concluded that phytate naturally present in TVP behaves similarly to phytate added to an otherwise phytate-free diet and that the reduced availability of Zn in TVP diets can be accounted for entirely by their phytate contents.
209 citations
TL;DR: A study has been made of the mechanism of the mutual antagonism between copper and zinc in rats and it appeared that copper displaced zinc from the protein after its synthesis had been induced by zinc.
187 citations
TL;DR: In this article, the degradation rate and outflow rate of protein particles from the abomasum of sheep were determined by rendering the protein supplement totally indigestible by a treatment with sodium dichromate, and the rate of outflow was greatest with sheep receiving dried grass and increased with increasing feeding level.
Abstract: Samples of soya-bean meal, groundnut meal, sunflower meal and fish meal were incubated in nylon bags in the rumens of sheep receiving either whole barley or dried grass. For the vegetable sources of protein the rate of disappearance of protein was greater when they were incubated in the rumens of sheep receiving dried grass than in sheep receiving whole barley. The rate of disappearance of fish meal did not vary between sheep fed whole barley or dried grass.Rate of outflow of protein particles from the rumen was determined by rendering the protein supplement totally indigestible by a treatment with sodium dichromate. The rate of outflow was greatest with sheep receiving dried grass and increased with increasing feeding level.The mathematical expressions of degradation rate and outflow rate were combined to give the total amount of protein degraded in the rumen for the grass and barley diets at two levels of feeding.The amino acid composition of residues left in the nylon bags after 9 h of incubation were shown to be almost identical to the amino acid composition of the original protein supplement, indicating that the composition of the amino acid in the undegraded protein entering the abomasum essentially resembled that of the supplements.
176 citations
TL;DR: Neutrophils isolated from the blood of selenium-deficient and selenia-adequate Friesian steers were shown to have similar abilities to phagocytoze cells of C. albicans, however, the neutrophils from the se lenium- deficient steerswere less able to kill ingested C.Albicans.
152 citations
TL;DR: A model is proposed for the facilitation and control of urea flux by wall-found ureolytic bacteria in sheep fed by intraruminal and intra-abomasal infusion and inversely related to rumen ammonia concentration.
Abstract: 1. The rumen urea concentration in gnotobiotic lambs lacking ureolytic bacteria was equal to that of blood. 2. Bacterial urease (EC 3.5.1.5) activity in sheep fed by intraruminal and intra-abomasal infusion was inversely related to rumen ammonia concentration. 3. A model is proposed for the facilitation and control of urea flux by wall-found ureolytic bacteria.
136 citations
TL;DR: 19 Indian children with liver disease were studied and 5 in whom a clinical and histological diagnosis of Indian Childhood Cirrhosis was made had massive orcein-staining deposits in liver cells.
133 citations
01 May 1979
TL;DR: In rats fed on beans the poorly digestible lectins were shown to react with intestinal cells in vivo and to cause a disruption of many of the brush borders of duodenal and jejunal enterocytes, suggesting toxicity was the result of ensuing systemic effects, such as for example the observed high N excretion possibly through increased tissue catabolism.
Abstract: In rats fed on beans (Phaseolus vulgaris) the poorly digestible lectins were shown to react with intestinal cells in vivo and to cause a disruption of many of the brush borders of duodenal and jejunal enterocytes. Although depressed to a certain extent, absorption still occurred, probably through the non-disrupted cells of the small intestine. In addition, abnormal absorption of potentially harmful substances, lectin-related or of bacterial origin, could also occur, possibly as a direct effect of the disruption caused by the lectins on the enterocytes. It is suggested that toxicity was the result of ensuing systemic effects, such as for example the observed high N excretion possibly through increased tissue catabolism.
127 citations
TL;DR: A technique is described for feeding young sheep for long periods entirely by the infusion of volatile fatty acids into the rumen and protein and other essential nutrients into the abomasum when the energy infused was twice the estimated requirement for maintenance, growth rate and nitrogen retention were essentially the same as in normally-fed sheep.
Abstract: A technique is described for feeding young sheep for long periods entirely by the infusion of volatile fatty acids into the rumen and protein and other essential nutrients into the abomasum. When the energy infused was twice the estimated requirement for maintenance, growth rate and nitrogen retention were essentially the same as in normally-fed sheep.
118 citations
TL;DR: The studies show that the ‘epithelial’ population can exist independently of the other two populations, that it is primarily responsible for urea digestion in the rumen and that it initiates breakdown of dead epithelial tissue.
Abstract: IT has been suggested that the bacterial flora of the rumen should be considered as three distinct, interacting populations—the bacteria of rumen fluid (the population which has been studied most extensively), the bacteria associated with food particles, and the bacteria adhering to the epithelial wall of the organ1. Until now, studies of the ‘epithelial’ population have been restricted to examination of postmortem samples of wall tissue and its attached bacterial flora2–5. A recently developed technique6 for feeding young sheep for long periods solely by infusion of protein and other essential nutrients into the abomasum, and of volatile fatty acids and bicarbonate buffer into the rumen, has provided us with an opportunity to study in isolation the role of the bacterial population of the wall in the ecomicrobiology of the rumen in the living animal. Our studies show that this population can exist independently of the other two populations, that it is primarily responsible for urea digestion in the rumen and that it initiates breakdown of dead epithelial tissue. Furthermore, our results point to an inverse relationship between ammonia concentration and ureolytic activity in rumen fluid, which may account for the control which ammonia exerts over flux of urea across the rumen wall7–9.
TL;DR: In the soft, gelatinous thickenings that appear to be the precursors of fibrous plaques, concentrations of plasma low-density lipoproteins and fibrinogen were three to four times higher than that in normal intima, but their concentrations of fibr in areas from more advanced plaques were not significantly higher.
TL;DR: It is concluded from this evidence that differences in kf for diets normally given to ruminants cannot be attributed to differences in utilization of volatile fatty acids.
Abstract: 1. Two experiments were conducted with lambs sustained entirely by intragastric infusion of volatile fatty acids (VFA), protein, minerals and vitamins. 2. In the first experiment to determine the effects of VFA on nitrogen retention four mixtures of VFA (B, C, D and E) were used containing acetic, propionic and butyric acid in the following molar proportions respectively: 45, 45 and 10; 55, 35 and 10; 65, 25 and 10; 75, 15 and 10. The level of infusion was 836 kJ/live weight0.75 per d and the design was a 4 X 4 Latin square with 14 d periods. There were no significant differences in the N balance between the different mixtures of VFA though mixture B tended to give the highest N retention. 3. Thirty-two lambs were used in the second experiment for measurements of heat production in closed-circuit respiration chambers. Six mixtures of VFA were used. These included mixtures B-E from Expt 1 and in addition two mixtures (A and F) containing acetic, propionic and butyric acid in the following molar proportions respectively: 35, 55 and 10; 85, 5 and 10. The heat production was measured both at 450 and 900 kJ/W0.75 per d, except for mixture F, where it was not possible to achieve a rate of infusion in excess of 675 kJ/W0.75 per d. 4. The energy required for maintenance was determined to be 0.45 +/- 0.02 MJ/kg live weight0.75 per d regardless of the mixture used. 5. The efficiency of utilization for fattening (kf) values for the six mixtures were 0.78, 0.64, 0.57, 0.61, 0.61 and 0.59 for mixtures A, B, C, D, E and F respectively. Only mixture A was significantly better utilized than the other mixtures. This mixture also gave the most efficient N utilization. 6. It is concluded from this evidence that differences in kf for diets normally given to ruminants cannot be attributed to differences in utilization of volatile fatty acids.
TL;DR: Eleven out of the 13 cultivars examined were highly toxic for rats in the raw state and two low-lectin bean varieties, Pinto III and Great Northern, had no appreciable disruptive effects on the intestines and were essentially non-toxic for rats.
Abstract: The chemical composition, lectin content and nutritional value of selected cultivars of kidney beans (Phaseolus vulgaris) were determined. Mainly due to different amounts of reserve globulins deposited, seed N content varied between 3.4 and 5.0%. The amino acid composition and the corresponding chemical score values of 40-60 however, were similar for all the beans, with the sulphur-containing amino acids limiting. Despite similarities in composition, 11 out of the 13 cultivars examined were highly toxic for rats in the raw state. These were all found to contain high concentrations of haemagglutinating lectins (over 10% of the total protein). On the other hand, two low-lectin bean varieties, Pinto III and Great Northern, had no appreciable disruptive effects on the intestines and were essentially non-toxic for rats.
TL;DR: In this article, the amounts of essential amino acids which minimized urinary N excretion when diets with barley as the only source of protein were given at the rate of 120 g/kg0.75 per d, corresponding to an increase in biological value (bv) from 0.51 to 0.86.
Abstract: 1. In five experiments, involving 142 female pigs weighing on average 33 kg, estimates were made of the amounts of essential amino acids which minimized urinary N excretion when diets with barley as the only source of protein were given at the rate of 120 g/kg0.75 per d. 2. With additions of lysine (4.0 g/kg diet) and threonine, (1.2 g/kg diet) to barley urinary N excretion decreased from 0.91 to 0.36 g/kg0.75 per d, corresponding to an increase in biological value (bv) from 0.51 to 0.86. 3. With these additions of lysine and threonine, there were no responses to additions of tryptophan, methionine or isoleucine, or to further additions of lysine or threonine, but addition of histidine significantly reduced N excretion. 4. No optimal addition of histidine could be determined; the mean rate of N excretion after addition of histidine (not less than 0.3 g/kg diet) was 0.27 g/kg0.75 per d, corresponding to a BV of 0.93. 5. There was a variation between pigs from different litters in their responses to added histidine. Those with low rates of N excretion on the unsupplemented diet did not respond to additions of histidine, but those with high rates did. 6. It is concluded that additions of only three amino acids can greatly improve the nutritive value of barley protein for the growing pig and that the amino acid composition of the supplemented protein closely approaches the ideal; it is also similar to whole-body tissue protein.
TL;DR: Hydrolytic rumen bacteria may require the higher NH3 concentration either for effective NH3 assimilation by an unknown mechanism involving alanine or for full expression of enzyme activity.
Abstract: The mean NH3 concentration in the rumen of sheep fed whole barley (0d8 kg/d) by continuous feeders was increased from 6d1 to 13d4 HIM by supplementing the feed with urea (30 g/kg). This change caused a 90% increase in the rate of degradation of rolled barley, and smaller increases in the rates of degradation of protein and plant fibre in the rumen. The total viable count and numbers of pectinolytic bacteria in rumen fluid increased with the urea supplement. Enzyme studies indicated that NAD-linked glutamate dehydrogenase was the main pathway of NH3 assimilation by rumen bacteria at both NH3 concentrations. Glutamate was the main free amino acid found in the rumen at low NH3 but, despite the low activity of alanine dehydrogenase and glutamate-pyruvate aminotransferase, alanine was the principal amino acid at high NH3 concentrations. Hydrolytic rumen bacteria may require the higher NH3 concentration either for effective NH3 assimilation by an unknown mechanism involving alanine or for full expression of enzyme activity.
TL;DR: In this article, changes in body composition during lactation were measured in 12 Border Leicester × Scottish Blackface ewes by serial slaughter at 12, 41 and 111 days of lactation.
Abstract: Changes in body composition during lactation were measured in 12 Border Leicester × Scottish Blackface ewes by serial slaughter at 12, 41 and 111 days of lactation Ewes suckled twin lambs and were given daily 1·6 kg dry matter of a complete diet containing 151 g crude protein and 10·2 MJ metabolizable energy/kg dry matterLive weights of ewes averaged 60·2, 58·9 and 55·8 kg at 12, 41 and 111 days of lactation respectively There were no significant changes in weights of stomach, small and large intestine and liverThe weight of body fat averaged 9·19, 2·28 and 1·19 kg at 12, 41 and 111 days respectively (P < 0·001) and weight of ash increased from 1·72 kg at 12 days to 2·30 kg at 111 days (P < 0·001) Water to protein ratios at the three stages of lactation were 2·94, 3·36 and 3·18 (P < 0·10) The energy value of weight loss varied from 68 to 17 MJ/kg, depending on the relative changes in total body water and fat Live-weight change was therefore a poor indicator of change in body energy during early lactationBody fat could be predicted from its combined relationships with live weight and total body water (residual sd ±0·70 kg), but when deuterium oxide space was used to estimate body water separate equations were necessary for early and later stages of lactation This was apparently due to differences between stages of lactation in the time required for deuterium oxide to equilibrate with water in the reticulo-rumen
TL;DR: In this article, four experiments were made during early lactation on individually penned Finnish Landrace × Dorset Horn ewes, each suckling two lambs, each of which was fitted with abomasal cannulae.
Abstract: Four experiments were made during early lactation on individually penned Finnish Landrace × Dorset Horn ewes, each suckling two lambs. In Experiment 1, 14 ewes of mean body weight 74 ± 2·4 kg received daily, 1·9 kg dry matter, 20 MJ of metabolizable energy and 300 g of crude protein from a diet (H) containing hay, barley and fish meal. Reduction of the daily crude protein intake of half the ewes to 225 g by replacing fish meal with barley (diet L) in week 2 of lactation resulted in a decrease (P< 0·01) in daily milk yield of 0·53 kg (17%) compared with no change for ewes remaining on diet H. The effect was reversed by returning the ewes to diet H at the end of week 3. In Experiment 2 the use of four ewes fitted with abomasal cannulae showed that the additional non-ammonia nitrogen reaching the abomasum when fish meal was given was used with an efficiency of 0·51 for the production of milk nitrogen. In Experiment 3, involving 20 ewes, a restriction in protein intake for more than 10 days in early lactation by replacing the fish meal with barley depressed subsequent milk yield. In Experiment 4, 24 ewes were given either fish meal, soya bean meal or groundnut meal as protein supplements. In early lactation fish meal was superior by 0·40 and 0·43 kg of milk per day to soya bean meal and groundnut meal respectively, and this was attributed to the greater quantity of non-ammonia nitrogen reaching the abomasum in the fish meal compared with the soya bean meal and groundnut meal supplements. The commercial significance of the results is discussed.
01 May 1979
TL;DR: Three classes of substances which can impair mineral utilization are organic factors which can bind essential minerals to form insoluble or indigestible complexes in the lumen of the intestinal tract and prevent their absorption.
Abstract: A list of mineral elements known to be essential to animals and dietary components which under the appropriate conditions modify either their utilization or apparent requirements is shown in Table I. Clearly, detailed discussion of all of these cannot be included in this review and thus a few examples will be briefly discussed to illustrate the many types of interactions that can occur. These can be broadly classified into three categories. First, there are situations when the presence of one element in excessive concentration can modify the utilization of another essential element, usually but not exclusively at sites of absorption. Second, there are factors which, while exerting no effect on the absorption of an essential element, may affect its subsequent utilization. The best examples of this type of interaction are the goitrogens which affect the metabolism of iodine. The third class of substances which can impair mineral utilization are organic factors which can bind essential minerals to form insoluble or indigestible complexes in the lumen of the intestinal tract and prevent their absorption.
TL;DR: In this paper, the effects on pregnant sheep of cadmium and excess dietary zinc, separately and in combination, were investigated and the possible mechanisms involved in these effects were discussed.
TL;DR: The optimum extent of processing appears to be the minimum required to avoid an unacceptably low digestibility and for cattle some processing is required to ensure adequate digestion but the optimum is that required to give entrance through the seed coats to microorganisms and digestive enzymes.
TL;DR: Fine structural changes in the liver during the prehaemolytic phase of chronic Cu poisoning in sheep were investigated in biopsy and post-mortem samples obtained from 24 Finn-Dorset × Suffolk ewe lambs.
TL;DR: Current evidence indicates that trace element antagonists influence both the absorption and the subsequent fate of essential and toxic elements in body tissues and these processes have to be taken into account when investigating the aetiology of disorders believed to be attributable to anomalies in trace element supply.
Abstract: Trace element deficiency and toxicity in animals induces a wide variety of clinical effects although few are sufficiently specific to permit diagnosis without supporting investigation of changes in tissue trace element content or of the activity of metabolic processes influenced by trace element supply. Study of such trace element dependent processes has shown that extensive changes often arise before overt signs of disease appear. Some of these subclinical effects have pathological consequences and thus cannot be ignored when seeking correlations between geochemical anomalies and disease incidence. Many past estimates of the quantitative requirements of animals for the essential trace elements are imprecise. Although recent work is providing clearer definition of requirements, many common dietary components have a marked influence upon the efficiency with which such elements can be utilized from the diet. Recent evidence indicates that such antagonists influence both the absorption and the subsequent fate of essential and toxic elements in body tissues and these processes have to be taken into account when investigating the aetiology of disorders believed to be attributable to anomalies in trace element supply. Their existence is not always detectable if attention is confined to the trace element analysis of body tissues or to the nature of clinical lesions. Provided the complexity of soil-plant-animal relations with respect to trace element supply is fully recognized in the interpretation of data, the geochemical approach to the initial recognition of areas associated with a high risk of anomalies in trace element supply to animals and man has considerable potential value. This is already apparent from investigations upon the incidence of trace element problems in animals. As yet, its validity for similar purposes in man is less fully established.
TL;DR: A study has been made of the effects of chloroform inhalation, Escherichia coli endotoxin injection and hydrocortisone injection on the absorption of a single intragastric dose of 65Zn by the chick and the increase in hepatic Zn concentrations in the stressed chicks was mainly associated with a protein in the cytosol identified as metallothionein.
TL;DR: Backfat thickness was also reduced by amino acid additions but failed to reach a minimum, while carcass fat, estimated by sepcific gravity, was least with the addition of 5.9 g L-lysine/kg, but continued to decrease up to the highest threonine concentrations.
Abstract: 1. Thirty-three diets were made by adding to ground barley combinations of L-lysine (0--6.0 g/kg) and L-threonine (0--3.0 g/kg), together with vitamins and minerals. Each was given to two female and two castrated male pigs during their growth from 25 to 60 kg. 2. Growth rate increased from 0.36 kg/d to a maximum of 0.65 kg/d with additions of 3.8 g L-lysine/kg and 1.8 g L-threonine/kg; these values and the maximum gains achieved were slightly higher for castrates than for females. Minimum values for food conversion ratio of 2.84 for castrates and 3.06 for females were achieved with similar amino acid additions to those giving fastest growth. 3. Carcass fat, estimated by sepcific gravity, was least with the addition of 5.9 g L-lysine/kg, but continued to decrease up to the highest threonine concentrations. Backfat thickness was also reduced by amino acid additions but failed to reach a minimum.
01 Sep 1979
TL;DR: It can sometimes be misleading to rely solely on the measurement of the concentrations of the toxic metals in tissues or body fluids in predicting the risk associated with a particular level of exposure to the metals.
Abstract: The classical approach to studies on the toxicity of metals has generally been to establish dose-response relationships and to search for a connexion between the intake of the metal, its accumulation in the body and especially in target organs, and the development of particular symptoms of toxicosis. On the basis of the results obtained, attempts have been made to establish maximum safe or permissible levels of the metal in water and foodstuffs. In the case of cadmium, for example, it is generally assumed that the first signs of Cd poisoning will normally be the development of renal failure and that this will only occur if renal Cd concentrations are around 200 pg/g. It is now apparent, however, that this approach does not take sufficient cognizance of the considerable influence of a wide range of nutritional and physiological factors on the susceptibility of animals to heavy metal toxicities (Bremner, 1974, 1978). The dietary intake of essential metals, including calcium, iron, zinc and copper, is of particular importance in this regard. For example, absorption of Cd is enhanced in animals receiving diets which are low in Fe or Ca (Valberg et al. 1976; Washko & Cousins, 1976). The lesions which develop under these circumstances can be especially severe and, moreover, are not always the same as those normally associated with chronic Cd poisoning. Thus, signs of Fe deficiency have appeared in Japanese quail within days of their receiving a diet with only 2.5-5 mg Cd/kg and long before any significant increase in renal Cd concentrations occurred (Jacobs et al. 1974). It follows, therefore, that it can sometimes be misleading to rely solely on the measurement of the concentrations of the toxic metals in tissues or body fluids in predicting the risk associated with a particular level of exposure to the metals. Moreover, one of the earliest signs that toxic metals may be adversely affecting the health of man or animals may be a disturbance in the metabolism of an essential element. In this paper particular attention will be given to the importance of the
TL;DR: In a natural population containing resistant individuals where the use of warfarin is discouraged the change in the frequency of resistance should reflect the relative fitnesses of the three possible genotypes, and the Rw2 allele does not act as a recessive lethal, although it must be extremely disadvantageous.
Abstract: Resistance to warfarin and an increased vitamin K requirement appear to be pleiotropic effects of the same allele (Rw2). In a natural population containing resistant individuals where the use of warfarin is discouraged the change in the frequency of resistance should reflect the relative fitnesses of the three possible genotypes. A large polymorphic population of rats was extensively poisoned with warfarin and the level of resistance monitored regularly for a period of 18 months after withdrawal of the poison. During this period the proportion of resistant animals in live-capture samples decreased significantly from approximately 80 per cent to 33 per cent. This decline is consistent with a hypothesis of reduced fitness of both Rw2Rw2 and Rw1Rw2 genotypes relative to Rw1Rw1 under natural conditions. The relative fitnesses of these genotypes were calculated using an optimisation method based on least squares analysis. These estimates were: Rw2Rw2 (0.46), Rw1Rw2 (0.77) and Rw1Rw1 (1.00). Homozygous resistant individuals were found in some of the samples, confirming that the Rw2 allele does not act as a recessive lethal, although it must be extremely disadvantageous. Some heterogeneity was observed in the proportion of resistant animals in samples taken from different areas of the farm building complex. This could reflect stochastic processes influencing the Rw2 allele frequency in small peripheral populations.
TL;DR: It was concluded that although the prolific ewes incurred a substantial energy deficit during late pregnancy, their intakes in late pregnancy were nevertheless adequate to support the high rates of accretion of protein and of minerals in the gravid uterus.
Abstract: The concentrations of dry matter, crude protein, fat and ash and of Ca, P, Mg, Na and K were determined for 22 sets of twin foetuses, 33 of triplets and 11 of quadruplets of known gestational ages within the range 55–145 days. In addition, determinations were made of the concentrations of dry matter, crude protein, fat and ash in their associated placentae and empty uteri, and of dry matter, nitrogen, energy and ash in the foetal fluids. The dry matter, crude protein and fat concentrations in the placentae increased with foetal age and decreased with increasing litter size. Ash concentrations were unaltered. There was no effect of litter size or foetal age on the concentration of nutrients in the empty uteri. Dry matter and nitrogen concentrations in the fluids increased with foetal age but were independent of litter size, whereas ash concentrations increased with litter size but not with age.The form of the mathematical model for foetal growth is considered in relation to the estimation of rates of accretion and the estimation of the differences in composition to be expected between foetuses that are heavy and others that are light relative to their age. When the weights of the foetal constituents were fitted by Gompertz equations extended to include foetal weight as an allometric term, the effects of litter size on foetal composition could be estimated from the foetal weights for each size of litter. Concentrations of dry matter and of most constituents in the foetuses became less as numbers of foetuses increased, irrespective of stage of gestation.A description of the changing composition of the growing foetuses was provided by specific growth rates calculated from the fitted equations. With minor exceptions, derived estimates of foetal concentrations of each constituent were found to agree quite well with most previously published estimates for ovine foetuses, but similar agreement on daily accretion rates was not to be expected in view of the sensitivity of such estimates to the choice of model for foetal growth. Rates of accretion in the gravid uterus increased up to about 5 weeks before parturition and tended to level off thereafter, but most of them still increased slightly over the last 2 weeks, even in ewes bearing triplets or quadruplets. Taking account of the changes in the maternal body of the ewes, it was concluded that although the prolific ewes incurred a substantial energy deficit, and could not have consumed sufficient of the diet to avoid this, their intakes in late pregnancy were nevertheless adequate to support the high rates of accretion of protein and of minerals in the gravid uterus.
TL;DR: It is suggested that the aetiology of the cell toxicity may involve a block in sulphur metabolism, possibly complicated in the caecum by absorption of endotoxins.
TL;DR: In this article, four young lambs fitted with cannulas at the pylorus and at the ileo-caecal junction were used to study the effects of weaning on digesta flow and mineral absorption.
Abstract: Four young lambs fitted with cannulas at the pylorus and at the ileo-caecal junction were used to study the effects of weaning on digesta flow and mineral absorption. Prior to weaning when milk alone was fed the small intestine was the major site for dry matter disappearance and for the absorption of Ca, P, Na and K. Both the small and the large intestine were, however, important sites for Mg absorption at this time. After weaning, when the lambs were fed a concentrate diet, at least two-thirds of the digested dry matter disappeared within the reticulo-rumen. The small intestine, however, still remained the major site for the absorption of Ca, P, Na and K. Most Mg absorption, in contrast, now occurred anterior to the pylorus and it would appear that the move from hindgut to foregut as a site for Mg absorption was directly associated with the introduction of dry feed and the development of fermentative digestion within the reticulo-rumen. Both before and after weaning the faeces was the major route for the excretion of Ca surplus to requirement and the faeces also became increasingly important as a pathway for P and Mg excretion once dry feed was given. The urine, in contrast, was consistently the major pathway for the excretion of Na and K.